1. Field of the Invention
The present invention relates to a wiring board that has a plurality of wiring films, which are provided between interlayer insulating films, and interlayer-connection conductor films, which extend through the interlayer insulating films and provide electrical connections between the wiring films at different layers, and that houses at least one bare semiconductor integrated circuit device. The present invention also relates to a circuit module having another semiconductor integrated circuit device and a passive component that are mounted on the wiring board.
2. Description of the Related Art
Wireless communication ICs (semiconductor integrated circuit devices) for transmitting/receiving high-frequency signals and ICs for processing high-speed digital signals are susceptible to noise radiated from the surroundings, and the ICs also can be radiation-noise generating sources relative to other devices.
Accordingly, in a conventional approach, such ICs are covered with conductive shield caps, which are connected to, for example, ground lines (i.e., are grounded), so as to be electrostatically shielded from other devices.
FIG. 1 illustrates a known example of a circuit module having a RF-IC (radio-frequency integrated circuit device), for example, for transmitting/receiving a high-frequency signal or for processing a high-speed digital signal. A shield cap is provided for the RF-IC to provide electrostatic shielding.
Reference character 101 indicates a wiring board, and 102 indicates interlayer insulating films, which are made of a synthetic resin. Reference character 103 indicates wiring films made of a conductor, such as copper. Reference character 104 indicates interlayer-connection conductor films, which extend through the interlayer insulating films 102 and which provide electrical connections between the wiring films provided at different layers. The interlayer-connection conductor films 104 are called via-holes, through-holes, or the like. The interlayer-connection conductor films 104 will hereinafter be referred to as “via-holes”.
Reference character 105 indicates an IC, which is mounted on one surface of the wiring board 101. Reference character 106 indicates a passive component (e.g., a resistor, a capacitor, a balun circuit, a crystal oscillator, or a filter), which is mounted on the surface of the wiring board 101. Reference character 107 indicates a RF-IC for, for example, transmitting/receiving a high-frequency signal. As described above, a shield cap 108 is provided to electrostatically shield the top and the periphery (lateral sides) of the RF-IC 107. Needless to say, the shield cap 108 is connected to a shield potential-point of a ground line or the like.
According to such a high-frequency circuit module, the shield cap 108 can prevent ambient noise from penetrating the RF-IC 107 and also can prevent the RF-IC 107 from becoming a noise radiation source to other devices.
Japanese Unexamined Patent Application Publication No. 2001-77537 discloses an alternative technology for providing electrostatic shielding. In the technology, a housing space for housing a bare IC is provided inside a wiring board, and shield wiring films are provided above and below the housing space inside the wiring board and are connected to a ground line. Thus, the IC within the housing space is electrostatically shielded by the upper and lower shield wiring films.
The known technology shown in FIG. 1, however, requires the attachment of the shield cap 108 for covering the IC (e.g., an RF-IC) 107 to provide electrostatic shielding, thus posing a problem in that it is difficult to achieve miniaturization.
In particular, a great demand exists for miniaturization of mobile telephones, mobile electronic devices, and the like, so that a great requirement also exists for high-frequency modules and the like for use therein.
Thus, since the known technology shown in FIG. 1, which requires the attachment of the shield cap 108, has difficulty in fulfilling the demand for miniaturization, it has a considerable problem.
Further, since the attachment of the shield cap 108 requires time and cost, the known technology has difficulty in meeting a demand for cost reduction.
The shield cap 108 also has a disadvantage in that it cannot electrostatically shield the bottom-side of the IC 107.
On the other hand, according to the technology disclosed in Japanese Unexamined Patent Application Publication No. 2001-77537, there is no need to attach the shield cap 108. An IC, such as a RF-IC, is housed in a housing space within a wiring board and is electrostatically shielded by wiring films of the wiring board. Thus, the technology facilitates miniaturization. Further, since there is no need for a process for attaching such a cap, the technology reduces time and cost, compared to the known technology shown in FIG. 1.
Additionally, the technology disclosed in Japanese Unexamined Patent Application Publication No. 2001-77537 is also advantageous in that it electrostatically shields not only the top side but also the bottom side of the IC.
Japanese Unexamined Patent Application Publication No. 2001-77537, however, does not provide electrostatic shielding against noise penetrating the RF-IC 107 from its side surfaces, which therefore does not provide a sufficient electrostatic shielding effect.